TRIGGER CRITERIA TABLE
The BATSE instrument can trigger on various energy ranges and photon count rate thresholds. This provides an opportunity to selectively monitor for transient events with characteristic spectral properties. For instance, the instrument is most sensitive to gamma-ray bursts when the trigger energy covers 50 keV to 300 keV, and it is most sensitive to terrestrial gamma-ray flashes when the trigger energy is 100 keV and above. Changes in count threshold can affect the triggering on event of a particular duration or characteristic peak flux. For instance, a high threshold on the 1024 ms timescale and a low threshold on the 64 ms timescale when triggering on the energy range 20 keV to 100 keV makes the instrument more sensitive to soft gamma-ray repeaters and less sensitive to solar flares. The table below gives the starting date and time for each trigger criterion used by the BATSE instrument. The first column gives the date on which the trigger was changed, the second column gives the truncated julian day (TJD) and the time of day in seconds (SOD) for the trigger change, the third column gives the channels used for triggering, the fourth, fifth, and sixth columns gives the trigger threshold above the background count rate in units of standard deviation on the 64 ms, 256 ms, and the 1024 ms timescales, and the final column gives the first trigger occurring under the new criterion. The channel numbers correspond to the following energy bands: channel 1 is 20 keV to 50 keV, channel 2 is 50 keV to 100 keV, channel 3 is 100 keV to 300 keV, and channel 4 is 300 keV and above. This table was last updated on May 1, 1997.
BATSE TRIGGER CRITERIA HISTORY ------------------------------------------------------------------- Date TJD/SOD Channels Thresholds Trig. # 64 256 1024 ------------------------------------------------------------------- 19-Apr-91 2+3 5.5 5.25 5.0 28-Apr-91 8367/5632 5.5 5.5 105 10-May-91 8386/75036 7.0 179 04-Jun-91 8411/68201 5.5 268 18-Aug-92 8852/56078 10.0 1852 24-Aug-92 8858/81762 8.0 8.0 1874 26-Aug-92 8860/78199 10.0 1881 14-Sep-92 8879/70852 5.5 5.5 1928 19-Sep-94 9614/57154 3+4 3175 31-Jan-95 9748/55085 1+2 6.0 6.0 6.0 3386 06-Feb-95 9754/69000 10.0 3405 17-Feb-95 9765/62185 3+4 4.5 4.5 4.5 3434 12-Apr-95 9819/56745 1+2 6.0 6.0 6.0 3504 10-May-95 9847/74116 10.0 3570 20-Jul-95 9918/73523 20.0 10.0 3672 21-Jul-95 9919/62439 10. 3679 24-Jul-95 9922/54971 1+2+3+4 26.0 6.0 6.0 3704 28-Jul-95 9926/66825 10.0 3713 05-Sep-95 9965/60364 5.5 5.5 5.5 3778 02-Oct-95 9992/77028 1+2 7.0 3843 23-Oct-95 10013/73672 2+3 5.5 3883 11-Dec-95 10062/77542 1 3.5 3942 18-Dec-95 10069/64796 4.0 4027 07-Jan-96 10089/62939 1+2+3 5.5 4263 05-Apr-96 10178/85399 2+3 5413 25-Jun-96 10259/53576 3+4 4.5 4.5 4.5 5520 29-Aug-96 10324/77818 2+3 5.5 5.5 5.5 5589 05-Nov-96 10392/70428 1+2 7.0 5657 01-Dec-96 10418/73555 1+2 5.5 5.5 7.0 5703 25-Feb-97 10504/80816 2+3 5.5 6102